The present invention relates generally to a signal transmission system implemented with optical fibers and related optical components. More particularly, this invention relates to an optical collimator lens.
Fiber optical collimator is the basic element commonly used for making different types of optical components and devices. A collimator lens is one of the major functioning parts for the collimator to transfer the divergent light from the optical fiber core into a collimated beam. Most of the collimators now available in the marketplace are implemented with a gradient index (GRIN) lens. The GRIN lens has an advantage that it can be conveniently placed in a tube. However, the coupling loss between a pair of collimators implemented with GRIN lenses increases quickly when the distance between the lens and the light source from the optical fiber increases. The coupling loss is 0.2 dB for a working distance less than 10 mm. The loss becomes greater than 0.5 dB for a distance of 100 mm and increased to 2 dB when the distance is increased to 140 mm. The reason of higher coupling loss with long distance is that the GRIN lens is typical designed for short distance application. Its complicated manufacturing process prevents it from flexible distribution of the gradient index profile. Additionally, the gradient index profile typically has distortion compared with curved surface of the conventional lens that increases the coupling loss in long working distance also. Some of the fiber optical devices have a long optical path and thus requiring a collimator with long working distance. However, with a long working distance, the coupling loss becomes a limitation when implemented with conventional collimator using the GRIN lens. The manufacturing of the GRIN lens involves toxic materials that causes higher cost and supply limitation.
Therefore, a need exits in the art of design and manufacture of fiber optical components and devices to provide new configurations and optical components for making an optical collimator that would be suitable for flexible working distance without being limited by great amount of coupling losses. Preferably, the new configuration and new optical component would be provided with low cost without requiring complicate manufacturing processes and safe materials. The conventional collimator lens is commercially available but that lens is not suitable for application in fiber optics mainly due to high reflection from the planar surface of the lens facing the light source on the fiber tips.
It is therefore an object of the present invention to provide a new design and configuration for manufacturing a collimator lens by implementing the lens as a Rod Lens. The Rod Lens is provided with a special operational characteristic that it has a flexibly adjustable working distance and can be extended to a long working distance. With this new and improved collimator lens, the working distance limitation is resolved and the aforementioned difficulties and limitations in the prior art can be overcome.
Specifically, it is an object of the present invention to provide a new design and configuration for manufacturing a collimator lens by implementing a Rod Lens manufactured with a glass rod. The Rod Lens is formed with a first end-surface formed as spherical or aspherical end-surface and a second end surface formed as inclined-planar end-surface. Preferably, the incline angle of the inclined-planar end-surface relative to the main axis of the glass rod is substantially eight degrees or less. The Rod Lens as disclosed in this invention can be conveniently and economically manufactured. The Rod Lens also provides an advantage of high return loss. The return loss the power reflected back to optical fiber where the light signal comes out. When an optical collimator is assembled, the fiber tip is placed around the back focal point of the collimator lens. As the light comes out from the fiber and strikes on the back surface of the lens, a portion of light is reflected from that surface, some part of reflected light enters fiber and propagates along the fiber to interfere with signal source. The return loss is the critical parameters for a fiber optic component and devices. The Rod Lens is formed with diameter substantially in the range of the diameter of a regular GRIN lens such that the manufacture processes applied for handling the GRIN lens can also be applied for the Rod Lens. For smaller working distance, the coupling loss is similar to that of the GRIN lens. The coupling loss of the Rod Lens of this invention is much smaller than the GRIN lens for longer working distance. In addition to the advantage of flexibly longer working distance with smaller coupling loss, the Rod Lens of this invention can be produced with much lower cost than that of the conventional GRIN lens.
Briefly, in a preferred embodiment, the present invention includes a collimator lens for collimating an incident light beam. The collimating lens includes an optical transmission rod substantially formed as an elongated cylinder. The optical transmission rod further includes a first end surface formed as a spherical end surface and a second end surface opposite the first end-surface. The second end surface formed as an inclined planar surface having an incline angle relative to the optical axis of the optical transmission rod for increasing the return loss to the fiber from the inclined planar surface. In a preferred embodiment, the inclined planar surface has an incline angle of substantially eight degrees or more or less.
In summary, this invention discloses a collimator lens having a first optical surface for focusing an incident light beam to a point immediately near a second end surface, wherein said end surface is formed to have an increased return loss.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures.